A female rebel commander with a formidable reputation has surrendered to Colombian forces, delivering a fresh blow to South America's last big insurgency.

Nelly Avila Moreno, known as Karina, left the jungle on Sunday after making a deal with the government to desert from the Revolutionary Armed Forces of Colombia (Farc). The guerrilla, 45, was under pressure from Colombia's US-backed security forces as well as her own family, who reportedly pleaded with her to quit before she was killed. As a senior rebel commander in Antioquia, a mountainous region in the north-west, Karina was implicated in numerous shootings and kidnappings and had a bounty of about £400,000 on her head.

Her surrender is a coup for the centre-right government's increasingly successful military campaign against Farc, a Marxist group whose four-decade old insurgency is now funded largely through cocaine trafficking and kidnapping.

"We have been after this woman who did such damage to Antioquia and the whole region of Uraba for a long time," the defence minister, Juan Manuel Santos, told RCN Radio. She and another guerrilla known as Michin were "nearly dying of hunger" when they handed themselves in, he added.

About a third of Farc members are women, of whom Karina was the most senior. She took command of the guerrillas in Antioquia two months ago when her immediate superior, Iván Ríos, was killed by one of his own bodyguards. The guard cut off Ríos's hand to claim a $1m government reward, a betrayal that underlined Farc's dwindling morale, manpower and territory. Other commanders have been killed in army and police raids.

Another incentive for Karina to surrender was her son, according to the daily El Tiempo, quoting an unnamed intelligence official. "She said she was tired of war and that harassment from the army was very strong." Two weeks ago President Álvaro Uribe publicly guaranteed her safety if she turned herself in.

Karina is likely to be tried for murder, extortion and terrorism in relation to ambushes against security forces and numerous kidnappings, including that of Oscar Tulio Lizcano, a congressman abducted eight years ago and still held in a jungle hideout.